Commutating system for electrical machines



July 10,1923; 1,46f,446

' C. L. A. M. LEBLANC COMMUTATING SYSTEM FOR ELECTRICAL MACHI NES Filed Sept. 15. l920 2 Sheets-Sheet 1 Fig. 1

IN VE/VTOR July 10, 1923. w 1,461,446 .C. L. A. M. LE BLANC COMMUTATING SYSTEM FOR ELECTRICAL MACHINES Filed Sept. 15 1920 2 Sheets-Sheet 2 //VI/E/V TOR $54 4%. 4M.

Patented July 10, 1923.

UNITED STATES PATENT OFFICE.

CHARLES LEONARD ARMAND MAURICE LEBLANC, OF PARIS, FRANCE, ASSIGNOR TO SOCIETE ANONYME POUR LEXPLOITATION DES PROCEDES MAURICE LEBLANC- VICKERS, or PARIS, FRANCE.

GOMZMUTATING SYSTEM FOR ELECTRICAL MACHINES.

Be it known that I, CHARLES LEONARD j A'flriA nD MXURIGE LEBLANc, a citizen of the heiii'iib-lic "of F rance, residing at 1 Boulevard id'e lffihtmorency, Paris, Seine, France, have "inuented certain new and useful Improveagents in Commutating Systems for Electri- Machines; and I do hereby declare the following to be a full, clear, and exact defscription of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanyingdrawings and to letters or fi ures of refe ence marked thereon, fwhich form a part of this specification. 4

The earliest electrical machines having com n'utators were rovided with metallic brushes but in general the commutation will be improved by substituting carbon brushes.

e impr vement in commutation is due to the fact that the Contact resistance of car bon is much higher tha that of cop er so that when a brush "simultaneously engages two consecutive segments of the commutator and thus short-circuits a coil of the armature, the stren th of the short-circuit curwill be reduced as the resistance of the conductor which constitutes the short-cirincreased.

I This advantage is, however, only obtained at the price of 'a considerable increase in the dimensions of the brushes and of the commutato'r in fact the energy dissipated at the time of the short-circuit is transformed into heat in that part of the brush which is in [contact with the commutator. Now graphit'e, a poorer conductor of electricity than copper is also a poorer conductor of heat; it

"follows therefore that the heat developed at the end of a graphite brush is less rapidly dlssipated throughout the whole of its mass than is the case with a copper brush, consequently to prevent a dangerous heating of the surface of the conductors and brushes only current densities of about one-third of those in copper brushes can be tolerated in carbon brushes.

The object of the present invention is to construct an improved type of commutator v and a system of brushes by means of which the short-circuit current can be reduced to such an amount'as may-be desired a d also the bulk of the energy of the short-(Zircon Serial No. 410,534.

current dissipated in the formof heat at a distance from the commutator.

In the accompanying drawings F ig, 1 illustrates diagrammatically a part of a com mutator embodying the invention developed into a plane.

Fig. 2 is a section of one of the 6011111111- tator segments.- I p v Fig. 3 is a section of a part of the commutator on the line X X, Fig. 1.

I*ig. this a diagrammatic view similar to Fig. 1 illustrating a modification.

5 is a section on the line Z, on, Fig. 4.

6 is a section on the line l 0, Fig. 4.

Fig'. 7 is a face View and Fig. 8 an edge view of an improved brush constructed according to the present invention.

Referring now to Fig. 1, the successive commutator segments are represented by the strips 6 f 6 f etc Each brush is divided into series ofelements a, Z), c, 0?, etc,

which are connected to the main current lead through resistances r r i respectively and are staggered in the direction of rotation. As two consecutive segments of the commutator oughtnot to be able to be short-circuited by a single element of the brush, the space which separates them ought to be wider than this element. In such a con'i'mutator the insulating segments would be almost as wide as the conducting seg ments which would result in a poor mechanical construction.

It would also be impossible to rotate such a commutator at high speed by reason of the centrifugal force.

In the present invention this difficulty is avoided by constructing the comn'iuratot: with segments separated as usual by thin insulation, but in which only alternate segments such as 6 e 6 are made use of; the

other segments 7, f not being connected to the armature and each of the segments being wider than a brush element. To preventthe intermediate conducting segments such as f from short-circuiting the resistances r r 7 T when two elements of the brush occupy respectively positions such as indicated at Z), d for example, these segments are divided as shewn at g and the sections thus formed are insulated from one another. IVith this construction with the element d in contact with the segment 6 and the elemerit a with the segment e as shew n, the

Inish such ascellulose acetate or by .theinterr n asele r y she n' i e consequently the resistances will be designed to reduce this loss as much as possible consistent with the other objects in view.

In any case as good commutation as may be desired can be obtained at the cost of a small expenditure of energy by regulating the size of the resistances.

A simple method of constructing the brushesconsists informing them of a-fbundle of thin metallic .pl atesinsulated trombone another either layer [of insulating var- :position of a a segment of insulating material such as mica or by a layer of oxide formed on the surface of themetal as in the'caseof aluminiumfor of duralumin. The upper porti ons of .the'plates areslitor slotted in a well known manner as shewn in Figs. 7 and 8 so as to form a resistance of which the amount depends on the number'of slots made in the plate.

The latter can moreover, if necessary, be made of a high resistance alloy such as ferro-nickel. l

The division of the intermediate segments asabove described is not practicable with the ordinary construction of commutator in which t ns ements are on y h ld by r g or binding at theirlends. According, to the invention, therefore, these segments are secured to the supporting bush throughout their whole length by providing at their lower part a dove-tail extension as shewn in section in Fig. 2, this extension being received in an insulated grooyeof corresponding form provided in the supportingbush s.

Fig. 3 clearly shews this method of construction, the insulation being indicated at W.

It is necessary to take special precautions to avoidchafing the insulation when sliding the dove ,-tail into its groove. For this purpose the commutator segments and dove-tails ma be made" of a" trapezoidal section in The seg h o e omm e-to a en :befi 's arran d i fihje des En nee w "one endangering the insulation and definitely secured in their finahpositionby uforcing hem th u .on ma Id en r I th m t- .7 2?.c es e a m chines the bars or strips which connect the commutator segmentsto the windings must be secured in such a manner as to resist centrifugal forces, particularly if these segmentsand connections are 'ofaluminium 0r duralumin as in such cases thestrength of the soldered jointscannot be relied upon. For this purpose each segment which is to be connected is provided with an extension in the form of adove-tail K (see Figs. 4, 5 and 6)." The connecting bar or strip 7) is terminated by stirrup g pierced by a hole into which the'dove-taihextension p is forciblypressed' and then soldered. This stirrup q is itself formed in a dove'rta-il shape externally and is received in an insulated recess of the same shape formed in a metallic disc R mounted on the shaft and in contact with the commutator bush 8." This stirrup i Wide o g or h ten on exert y centrifugal forcecn the bar pane which is transmitted to it',' to spread over 'a sufiiciently large surface so that the insulation t will not 7 be crushed between stirrup and the wallof the recess Th jmei'm na, o thec ommutet ise f c ed without difliculty because the recesses provided inthediscvR for the stirrupsjK pei-mit IQ he a y Pas g 10 he dove-ta ls t structions since in cas'ethere will be the advantage of using metallic brushes instead or carbdnbrushes'; i 'i The present invention whi h jean be used n a le es if esiie l ia nliceble 0 t emlectrical machines having very highrotational speeds." I i In practice, inorder that the commutator s gments shall be able to resist the centrifue ce and notw ths d n tha the problemis simplifiecbby the substitution ,of duralu'min for copper in the ,m iilufacture of the commutator segments, the commutator can only be given a small dimension. 1e result is that if the normal number of segments "are provided these must be ,very narrow and their manufacture difficult, in order, t to Qb ei flpraet cable c n u tion the number of seg'ments is and conseqnently'the' difference of potential between two adjacent segments is increased. In this case the difficulties of'commutation are such that they'cannot be over'conie'when using brushes'of-the eediaa'rytype.

' Iti's obvious that the pr es'ent invell i n is not limited only to the co ri'ibination'b the commutatofandbrush system has been deseribed'abotebat th t it also xt ds commutator cylinder provided with a plurality of commutator segments, a plurality of low resistance brush elements electrically connected together and arranged in circumferential stepped relation with respect to each other for cooperation with said cylinder and each of said brush elements having a resistance in series therewith, alternate segments of said cylinder being connected to the armature windings oi the machine and the intermediate segments each being inactiv and divided into a plurality of sections which are insulated from each other and from said alternate segments, each or said sections being disposed in the path of one of said brush elements, whereby the individual brush elements are insulated from each other at the commutator, but electrically connected through said resistances.

2. A commutator comprising alternate segments adapted for connection to an armature winding, intermediate segments each divided into several insulated sections by slots perpendicular to the axis of the commutator and a supporting brush to which all the segments are secured by longitudinal clove-tails which together with the segments are trapezoidal in section substantially as and for the purpose specified.

I 3. A commutator cylinder comprising, a bushing, a plurality of commutator segments carried thereby, a plurality of connectors for certain of said segments adapted to be connected to the armature windings of the machine, each of said connectors being provided with an eye portion adapted to embrace a projection carried by a segment, and a disk mounted adjacent to the end of said bushing and having a plurality of recesses therein adapted to receive the eye portions of said conductors to maintain them against radial displacement.

1. in electrical connection between a com mutator segment and the terminal of an armature coil consisting of a bar or strip terminated by a stirrup-shaped piece having an orifice adapted to receive an extension of a commutator segment and a disc mounted acent to the end of the commutator, said disc having a dove-tail recess in which the stirrup-shaped piece is located.

5. A commutator cylinder comprising a .bushing provided with a plurality of longitudinally extending dove-tail slots in the periphery thereof, alternate slots being tapered in one direction and the intermediate slots being tapered in the opposite direction and a plurality of oppositely tapered commutator segments provided withtapered dovetail projections for cooperative engagement with said slots, adjacent segments being adapted to be slid into position in wedging' engagement with each other from opposite directions.

In testimony that I claim the foregoing as my invention, I have signed my name.

CHARLES LEONARD ARMAND MAURICE LEBLANC. lVitness:

PETER PETERSEN; 

